Project Summary Vertebrate embryo body plan is established through cell-cell interactions driven by a small number of signaling pathways. The knowledge of these embryo-derived molecules and pathways has been instrumental for in vitro differentiation of mouse and human pluripotent stem cells and serves as a basis for tissue engineering. In amphibians, signaling from Wnt, BMP, FGF and Nodal-related ligands results in the formation of the Spemann organizer and subsequent tissue patterning. Many other extracellular factors regulate the time, location and level of these signaling events, and their discovery and analysis remain an important goal of basic developmental biology. This application focuses on the analysis of pinhead (pnhd), a conserved gene that we identified in a screen for Wnt target genes. Overexpression and depletion experiments suggest roles of pnhd in axial patterning, but its mechanism of action is currently unknown. Other preliminary studies show that Pnhd is a secreted protein that modulates Wnt- and BMP-dependent signaling in a region-specific manner. Based on this evidence, Pnhd is hypothesized to function as a new context- specific modulator of embryonic pathways. The proposed experiments will test this hypothesis by characterizing the developmental roles and functional effectors of Pnhd that are relevant to vertebrate axis specification and anteroposterior patterning. Other studies will address the molecular basis of the context-dependent effects of Pnhd on Wnt signaling. The mechanism of Pnhd action will be investigated using Xenopus embryos, in which biochemical and cell biological approaches can be combined with rapid functional analysis in the context of an intact animal. These studies will contribute to further understanding of signaling networks leading to body plan specification and patterning during early development. Since Wnt and BMP pathways have been implicated in many human cancers, the proposed experiments will unravel novel molecular mechanisms that operate during normal embryonic development and become frequently disrupted in disease.